data published by Lucke et al. (2009), with the TTS to PTS extrapolation following the methodology outlined by Southall et al. (2007). The ranges for the onset of auditory injury in pinnipeds are based on the injury criteria by Southall et al. (2007) and are founded on data for a harbour or common seal Phoca vitulina (Kastak et al. 2005). It should be noted that prolonged exposure to repeated hammer strikes would increase the range over which injury might occur as described in Section 9.4.6.


99.


Potential ranges for the onset of instantaneous auditory injury for marine mammals during impact piling at East Anglia THREE are indicated in Table 9.6 to Table 9.9. Based on the injury criteria from Southall et al. (2007) the potential ranges where an instantaneous onset of auditory injury may occur span less than 500m for mid- frequency cetaceans, low-frequency cetaceans and pinnipeds in water. Assuming the sensitive receptor responds to the onset of pile driving by swimming away from the acoustic source (JNCC 2010), the potential for the onset of auditory injury would be expected to be mitigated by the 500m mitigation zone. For harbour porpoise the equivalent estimate is less than 1,000m from the pile, and is shorter for the lower hammer strike energies, with impact ranges no more than about 500m from the pile for hammer blow energies up to at least 2,300kJ (Table 9.6). Assuming a minimum 20 minute soft-start, a harbour porpoise swimming away at 0.5m/s (considered as slow, cruising swim speeds for harbour porpoise (e.g. Otani et al. 2000; Akamatsu et al. 2007)) would swim a distance of 600m. Considering this movement away from the source, and given that the 2,300 kJ hammer strike energy would not be exceeded during the minimum soft-start period, an instantaneous onset of auditory injury for harbour porpoise may be expected to be mitigated by the soft-start.


100. There are no known cases where marine mammal mortality has been reported as a direct result of noise exposure from windfarm construction or other acoustic sources of similar characteristics and SL. The predicted noise levels in close proximity to the pile are comparable to those estimated for the onset of auditory injury and mortality would only be expected at noise levels substantially above those necessary to cause auditory injury. The pile driving installation is thus unlikely to result in radiated noise levels sufficient to cause instantaneous mortality in marine mammals beyond a few metres from the pile, (Richardson et al. 1995 (converted from Yelverton et al. (1975) for marine mammals)).


Preliminary Environmental Information May 2014


East Anglia THREE Offshore Windfarm Appendix 9.1 Underwater Noise Modelling 36


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